This is kind of missing the point of the festival!
Take it you already have tickets, as they sold out long ago. Your ticket includes entry to the campsites. Buy a tent. A cheap one that you won't mind be stolen, destroyed by rain or caught on fire.
There are companies that provide "posh" tents or yurts at Glastonbury, and other companies that will provide a pre-erected "basic" tent in a special area, so you won't have to worry about taking your own tent.
All of this should be on the Glasto website, or you might have to do a google search for companies that provide tent (or yurt) accomodation at UK music festivals.
But why bother with a hotel or B&B? The Glastonbury Festival is actually held miles away from Glastonbury and the nearest village is actually Pilton.
No hotels in Pilton, but if there are B&B's they were probably booked up months ago.
There's no harm in googling "B&B's in or near Pilton" though.
P.S. and as mentioned above - you do have a ticket for festival???
At this stage, every hotel, B&B and rental cottage in the area will be booked up. That was probably the case in October, when tickets sold out in less than 2 hours.
Assuming you have a ticket, you should visit this site: http://www.glastonburyfestivals.co.uk/ for information about the festival, and you should visit Milletts to buy a tent, a sleeping bag, and some camping equipment.
The tickets were ALL sold within 1hr 27 minutes of being released on sale, back in October.
There are dozens of other festivals though... depends what your musical interests are?